High frequency apparatus



March 15, 1966 c. s. BIECHLER ETAL 3,240,983

HIGH FREQUENCY APPARATUS Original Filed Jan. 9, 1961 47 64 64 ENTORS A soscA c. u TROM ,5 ::Z9 BY M91 h ORNEY United States Patent Oflice3,24%,983 Patented Mar. 15, 1966 3 Claims. (or. 315-539 This applicationis a divisional application of U.S. Serial No. 81,455, filed January 9,1961, by Charles S. B-iechler et al., and assigned to the same assigneeas the present invention.

The present invention relates in general to high frequency tubeapparatus and, more specifically, to a novel high-frequency,high-powered, air-cooled, long-life velocity modulation tube ofrelatively small size and weight.

Heretofore, multicavity high-power klystron amplifiers which are capableof amplifying, for example, frequencies of about 8000 megacycles werewater-cooled and had a beam-guidance magnetic field produced byelectromagnets. The water-cooling insured low temperature operation ofthe tube parts, especially the collector and the tube tuning parts,while the electromagnets constrained the electron beams to theirrequired paths to keep the body currents low. The use of suchwater-cooling and electromagnets resulted in relative ease of klystrondesign and substantial over-all weight increase, the electromagnet, forexample, adding between 60 to 70 pounds to the klystron tube which, byitself, weighed between 3 to 6 pounds.

The present invention provides a high power multicavity klystronamplifier capable of delivering continuous output power in excess of onekilowatt at frequencies of, for example, about 8000 rnegacycles whilebeing repeatably tunable through a 500 megacycle band. The klystron hasa beam-guidance magnetic field produced by a permanent magnet, therebyeliminating the need for an electromagnet and its power supply. Theklystron is air-cooled to reduce the weight and thus lend itself moresuitable for transportable communications use. For example, the over-allweight of one tube including magnets made in accordance with the presentinvention is about 40 pounds. In order that the klystron have a highamplification factor, the klystron has a number of successive tunableintegral resonant cavities, for example, four. To enable the mosteflicient use of the permanent magnet, the cavities are made narrow toensure the shortest magnet gap spacing and thus the strongest possiblemagnetic field. Also, since the distance between the input and outputcavities is short, a novel waveguide coupling arrangement is providedfor the klystron which allows the body of the tube to be efiicientlyair-cooled. In addition, the electron gun has a novel constructionwherein the cathode emission is increased in order to produce greaterhigh-frequency power.

The principal object of the present invention is to provide a novelhigh-frequency, high-power, high gain amplifier tube having a long lifeand exceptionally broad frequency tuning range, which tube is preferablyair-cooled and has a permanent magnet for producing a beam-guidancefield.

Another feature of the present invention is the provision of a novelwaveguide coupling means which couples high frequency energy into acavity resonator and from a cavity resonator through apertures facing inthe same direction.

Other features and advantages of the present invention will becomeapparent upon a perusal of the following specifications taken inconnection with the accompanying drawings wherein:

FIG. 1 is an elevation view in partial section of a novel klystronembodying the present invention,

FIG. 2 is a partial longitudinal section view of the klystron body whichhouses the high frequency interaction means,

FIG. 3 is a partial view of the klyst-ron taken along line 3-3 of FIG.2, and

FIG. 4 is a detailed view of the flexible wall enclosed by circle 4-4 ofFIG. 3 shown rotated Referring now to the drawings, there is shown aklystron amplifier including an electron gun assembly 11 for projectingan electron beam through the klystron body section 12 which houses thehigh-frequency tunable cavity resonators and a collector assembly 13 forcooling the electrons after they have passed through the body section12. The cavity resonator tuning means includes the tuning screws 14which are accessible on one side of the body section 12. Thehigh-frequency signal to be amplified is coupled through a waveguide 15into the first cavity resonator 16 in body section 12 through anaperture 17 disposed on the opposite side from the tuning screws 14while the amplified high-frequency signal is coupled out from the lastcavity resonator 18 through an aperture 19 into an output waveguide 21.Two other cavity resonators 22 and 23 are disposed between resonators 16and 17. Cooling fins 24 are disposed on the two remaining opposite sidesof the klystron body section 12 to provide sufiicient cooling surfacefor the klystron body.

This klystron utilizes a magnetic field guidance for the electron beamas the beam passes through the cavity resonators, this field beingsupplied by a permanent magnet means including two substantiallyhorseshoe sections or halves (not shown) arranged to mate with the polepieces 26 and 27. To ensure the strongest possible magnetic fieldbetween pole pieces 26 and 27 the over-all distance from input cavity 16to output cavity 18 is made as short as practicable. This isaccomplished by making the resonant cavities 16, 22, 23, and 18 asnarrow as possible while still insuring their capability of resonatingat the proper frehuencies. As a result, the total space into which thewaveguides 15 and 21 must fit is limited. The waveguides are fixed toone wall 28 of the body 12 and since the length of body 12 is short theyare disposed adjacent to each other with partition 29 separating thetwo. When waveguides are disposed adjacent each other, additionalsections cannot be satisfactorily added since there is no room on theexterior of the waveguides for placing adequate flanges to which suchsection may be attached. It the flanges are not adequate, high-frequencyenergy will radiate from the output waveguide sections into the inputwaveguide sections, and noise will be produced in the system.

The present klystron has a novel arrangement for the input and outputwaveguide which is shown in FIG. 3. The waveguides 15 and 21 extend fromthe wall 28 of body 12 so that a wedge-shaped transition zone 31 isformed at the end of the waveguide 21 just exterior of its couplingaperture 19, and a similar wedge-shaped transition zone 32 is formed atthe end of the waveguide 15' just exterior of its coupling aperture 17.The Waveguides 15 and 21 extend in a different angular direction fromwall 28. Therefore, at a short distance from the body 12 there is ampleroom around the waveguide so that flanges 33 and 34 can be placed onwaveguides 15 and 21 respectively and a suitable vacuum tighthighfrequen-cy window (not shown) is placed in each flange.

As mentioned above, this tube is capable of being tuned over a broadband. Therefore, the cavities are tuned by making one narrow side wall36, 37, 38, and 39 in each cavity 16, 22, 23, and 18, respectively,flexible so that the walls are movable toward and away from the electronbeam which passes through drift tube sections 41, 42, 43, 44, and 45.Since the tube must have broad band tuning, the walls 36, 37, 38, and 39must be capable of flexing over a considerable distance. Therefore, inorder that the tube can be tuned repeatedly without the walls incurringfatigue failure before the tube life has expired, the flexible walls aremade very thin and from a very ductile and good-conductor metal, such ascopper. Even though the flexible wall is made of a good conductor, thereis considerable high-frequency heating of the flexible walls. Since theyare thin this heat flow path is small, and therefore the walls willbecome very hot. A heat sink in the form of a relatively massive metalbar 47 is placed on the center of each wall 36, 37, 38, and 39 so thatthe heat energy now travels a path through the walls which is half aslong, thereby helping to cool the walls. The edges of the walls 36, 37,38, and 39 being fixed to end Walls 48 and 49 of cavity 16, end walls 49and 51 of cavity 22, end walls 51 and 52 of cavity 23, and end walls 52and 53 of cavity 18, respectively, are adequately cooled, but the bars47 being dispersed within a vacuum need an efiicient heat path to keepthem cool. Although each bar 47 is connected to a tuning screw 14 whichis outside the vacuum envelope, the heat path is very long and does notprovide efiicient cooling. This heat path from the bar 47 may be tracedthrough guide 54 which is supported within the vacuum envelope of theklystron on sapphire bearing rods 56 and adjustment rod 57 which isthreaded at one end into internal screw threads on the tuner screw 14.Screw 14 also has external screw threads which coact with the body 12.The internal screw threads have a different pitch than the externalscrew threads, so that rod 57 will move into and out of the body section12 as the screw 14 rotates, causing the guide 54 to follow. A tubularbellows 59 is disposed around the rod 57 to provide the necessaryflexibility in the vacuum wall of the klystron. Since the total lengthof the body 12 is short the tuning screws 14 are staggered. Thus, inorder to cool the bar 47 effectively, additional flexible members 62 and63 which guide the heat to the end walls are disposed behind flexiblewalls 36, 37, 38, and 39.

For ease of construction, walls 36, 37, 38, and 39 are composed of onecorrugated metal sheet with the areas 64 (FIG. 4) which are showndisposed between end walls 48, 49, 51, 52, and 53 and associated bars 47preferably are made thinner than the areas 66 which are brazed to theend walls and bars 47 since most of the flexing of the wall is performedin these areas 64. The corrugated metal sheet with two differentthicknesses allows the metal to be more readily brazed than a corrugatedsheet metal having one very thin thickness which must correspond to thethickness of areas 64. Flexible members 62 and 63 are made similar tothe corrugated sheet metal which forms flexible walls 36, 37, 38, and39.

Capacitive tuning horns 67 (FIG. 3) are attached to each end of bars 47making two horns for each cavity 16, 18, 22, and 23 which furtherincreases the tuning rate of the cavity as the flexible walls are moved,thereby increasing the tuning band of the klystron tube.

The tube has a novel electron gun structure which aids in increasing itshigh-frequency power. The cathode 68 is preferably made of poroustungsten and impregnated with suitable oxide mixes, as is well known inthe art, with a pancake type heater 69 suitably supported behind thecathode. A focusing electrode 71 is disposed in front of the cathode 68so that the part of the cathode disposed around its periphery isshielded from the positive potential of the anode 41. This outside partof the cathode is difficult to maintain at the uniform temperature atwhich the central portion 68' is maintained, and therefore the emissivecurrent density of this part is lower than the emissive current densityof the central portion 68. This arrangement of the focusing electrodepermits only the electrons emitted from portion 68' to be focused intothe beam, thereby increasing the current density of the beam.

A high density beam when it is collected by the collector liberateslarge amounts of energy as heat on a smaller area thereby causinglocalized melting of the collector. In order not to melt the collector,the energy must be spread over a large area. This is accomplished byshaping the magnetic field so that it helps defocus the beam in thecollector region as well as guide the beam through the body 12. Themagnetic pole pieces 26 and 27 (FIG. 4) which are disposed at each endof the drift space are made with apertures 73 and 74, respectively,through which the beam passes. Aperture 73 being larger than aperture 74has disposed therein drift tube section and anode 41 made ofnon-magnetic material. This allows the magnetic lines of force topenetrate into the gun assembly 11, thereby increasing the focusingcharacteristic of the electron gun and also, because the electrons aretraveling substantially parallel to the magnetic field disposed betweenthe region from the cathode 68 to the anode 41 less noise is produced inthe system. The beam rapidly spreads after it passes through aperture74. Since aperture 74 is small, the magnetic field therein issubstantially transverse and there is no or very little magnetic fieldin the collector. Though the beam spreads, the collector must still becooled by a series of radial fins 76 which are orientedcircumferentially around the anode. The fins 76 may be either a seriesof thin washers, brazed to the collector, or a thin member helicallywound around and brazed to the collector. The fins are enclosed by acylindrical member 77 which has four openings 78 extending its fulllength and disposed at 90 intervals around the member 77. Cooling air isintroduced into two diametrically opposed openings 78 and exhaustedthrough the remaining two openings. This arrangement provides amultitude of short paths for the cooling air and consequently the amountof energy necessary to drive the cooling air is low. Member 77 may bemade of magnetic material to further bypass the magnetic field from thecollector.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a linear beam high-frequency amplifier, an electron gun forproducing and directing an electron beam along a central beam axis, acollector for collecting said electron beam, and a high frequencyinteraction means positioned between said gun and said collectorcomprising a plurality of cavity resonators, said electron gun,collector and plurality of tunable cavity resonators lying along anddefining an elongated central axis along which said electron beamtravels between the electron gun and collector, the respective endcavity resonators of said plurality of cavity resonators disposed at theends of said interaction means each having a coupling aperture facing inthe same direction the respective axes of said coupling apertures beingsubstantially perpendicular to said central axis along which saidelectron beam travels, and a waveguide coupled to said each end cavityresonator through said coupling aperture therein, each of saidwaveguides being disposed at an acute angle to the axis of itsrespective coupling aperture forming a transition zone in saidwaveguides exteriorly of said cavity resonators said Waveguides eachdefining a central axis, said central 5 axes of said waveguides lying ina pair of spaced parallel planes disposed normal to the central beamaxis of said amplifier.

2. The amplifier defined in claim 1 wherein said plurality of cavityresonators are tunable and wherein said cavity resonators include tuningmeans disposed at 180 space rotated portions of said cavity resonatorswith respect to said coupling apertures.

3. The amplifier defined in claim 1 wherein the respec- 90 anglesrelative to each other.

References Cited by the Examiner UNITED STATES PATENTS Crapuchettes eta1. 315-539 HERMAN KARL SAALBACH, Primary Examiner.

tive axis of said waveguides are disposed at substantially 10 ELILIEBERMAN Examiner S. CHATMON, IR., Assistant Examiner.

1. IN A LINEAR BEAM HIGH-FREQUENCY AMPLIFIER, AN ELECTRON GUN FORPRODUCING AND DIRECTING AN ELECTRON BEAM ALONG A CENTRAL BEAM AXIS, ACOLLECTOR FOR COLLECTING SAID ELECTRON BEAM, AND A HIGH FREQUENCYINTERACTION MEANS POSITIONED BETWEEN SAID GUN AND SAID COLLECTORCOMPRISING A PLURALITY OF CAVITY RESONATORS, SAID ELECTRON GUN,COLLECTOR AND PLURALITY OF TUNABLE CAVITY RESONATORS LYING ALONG ANDDEFINING AN ELONGATED CENTRAL AXIS ALONG WHICH SAID ELECTRON BEAMTRAVELS BETWEEN THE ELECTRON GUN AND COLLECTOR, THE RESPECTIVE ENDCAVITY RESONATORS OF SAID PLURALITY OF CAVITY RESONATORS DISPOSED AT THEENDS OF SAID INTERACTION MEANS EACH HAVING A COUPLING APERTURE FACING INTHE SAME DIRECTION THE RESPECTIVE AXES OF SAID COUPLING APERTURES BEINGSUBSTANTIALLY PERPENDICULAR TO SAID CENTRAL AXIS ALONG WHICH SAIDELECTRON BEAM TRAVELS, AND A WAVEGUIDE COUPLED TO SAID EACH END CAVITYRESONATOR THROUGH SAID COUPLING APERTURE THEREIN, EACH OF SAIDWAVEGUIDES BEING DISPOSED AT AN ACUTE ANGLE TO THE AXIS OF ITSRESPECTIVE COUPLING APERTURE FORMING A TRANSITION ZONE IN SAIDWAVEGUIDES EXTERIORLY OF SAID CAVITY RESONATORS SAID WAVEGUIDES EACHDEFINING A CENTRAL AXIS, SAID CENTRAL AXES OF SAID WAVEGUIDES LYING IN APAIR OF SPACED PARALLEL PLANES DISPOSED NORMAL TO THE CENTRAL BEAM AXISOF SAID AMPLIFIER.